1. Field of the Invention
The present invention relates to an image processing apparatus having a document read section, and more particularly to an image processing apparatus of the type that image information is converted into electrical signals for image process.
2. Description of the Prior Art
Rapid developments in the field of image sensors such as CCDs and record devices such as ink jet devices have recently been made. With the advent of an elongated and multi-construction type device having a high resolution more than 400 dot/inch, it has become possible to realize, by using a digital type image forming apparatus, an image as good as that formed by using an analog type copy apparatus.
A technique of spatial filtering for sharpening images of such as TVs and CT scanners is also known in the art.
The spatial filtering technique is effective for the digital image forming apparatus to compensate for or correct: such as quantization errors in analog/digital converted image data; unfocussed images caused by area/density modulation through a dither method for performing gradation representation of binary coded images; or noises in the images.
A simple construction of a digital image forming apparatus is realized by using an image sensor and write head each having the same length as that of the object document. However, in case of a large size object document and color copy, the apparatus becomes extremely expensive because of a low manufacturing yield and the hardship in maintenance. Therefore, a scan method low in cost and good in performance has been considered heretofore, wherein an image sensor and write head of a smaller length are used for respectively reading and writing the same number of pixels. A partial image having a constant width is formed by main-scanning the image in the longitudinal and perpendicular directions, and the whole image is formed by repeating the main-scan followed by a sub-scan in the direction perpendicular to the main scan. In this scan method, however, the image is divided at the discontinuous portions between the main scans, which necessitates the need of storing some portion of the bottom pixel data required for processing the top pixel data or bottom pixel data of the image sensor and write head. Particularly, when a high resolution and large size image is desired, a large memory capacity is required which results in an extremely expensive apparatus.